The stocks of gasoline stored in service station tanks should be accurately and frequently measured to have control of the inventory as well as to detect theft and leakage losses. The most frequent way for measuring the stock of gasoline has been the use of a calibrated pole which is inserted into a gasoline tank by an operator to measure the depth of the gasoline in the tank. This depth reading is then converted to volume. However, this method leaves much to be desired. The accuracy of such measurements is not good. It is difficult to detect a loss of gasoline in a tank due to a slow leak since this could be masked by the actual withdrawal of fluid from the tank. There further needs to be unattended monitoring at frequent intervals to detect theft losses. There is also a need to measure both the level of gasoline and the level of water in the tanks to determine if the gasoline is being replaced with water.
In addition to the calibrated pole, gasoline stocks have been measured by a mechanical float indicator, echo sounding and capacitance measurements. However, all of these measurements suffer from lack of accuracy, mechanical complexity or the need for manual operation. In view of these difficulties there exists a need for a fluid measurement gauge which can periodically and accurately determine the level of fluid in a tank without manual intervention.